Yesterday I fully uninstalled and reinstalled Windy application (so all stored data were deleted, not only the cache; performed new widget setup etc).
After this, sync and battery drain issues disappeared...

It seems something stored in data from previous versions caused mentioned issues with the widget.

And it seems issue is caused by update downloaded from PlayStore in past 4 days. Before, windy used less than 1% battery, last days consumes ~18%...

@Suty I have similar issues on Samsung S22 (with latest software). Widget seems to be broken, fails to update. I noticed that by unusual battery drain past days. When I delete widget, cleared caches etc... nothing helps. Hints you're providing aren't helpful.